A caricature of Obama as Heath Ledger’s garish, pasty-faced Joker from “The Dark Knight” is appearing on the Facebook pages of many an Obama critic these days. And, as is depressingly common, there are Democrats who cry “racist!”

The Washington Post devoted several hundred words on the topic: “[The] poster is ultimately a racially charged image. By using the ‘urban’ makeup of the Heath Ledger Joker, instead of the urbane makeup of the Jack Nicholson character, the poster connects Obama to something many of his detractors fear but can’t openly discuss. He is black and he is identified with the inner city, a source of political instability in the 1960s and ’70s, and a lingering bogeyman in political consciousness despite falling crime rates.”

Say what?!

The mental contortions needed to make this link are flabbergasting. The point of the Joker cartoon is as obvious as can be: The president of the United States — or his policies so far stated — is a comic-book villain, stealing your money. You may not agree with that — but to suggest that caricature is out of bounds undermines the ideals of free speech and political expression.

No, Obama’s election did not make our nation colorblind. But Obama’s defenders are doing their president and themselves a great wrong. For when real racial injustices surface, the country — so numb to false outrage from Harvard professors and propaganda posters — will shrug it off. “Racist” is diluted to just another insult, robbed of all its shame. The Joker, unfortunately, will be on them.